Review of Lightweight Deflectometer for Routine in Situ Assessment of Pavement Material Stiffness

Abstract

• This is a journal article. It was published in the journal, Transportation Fleming, Frost, and Lambert 2 ABSTRACT The use of a portable lightweight deflectometer (LWD) for construction quality control or material investigation for earthworks and road construction is increasing around the world. This paper reviews the LWD as a field evaluation tool, discusses the test variables and data quality and concludes both on its usefulness and also its limitations for a variety of earthwork and road assessment scenarios. The paper aims to provide a state of the art reference document for LWD users, consultants, material specifiers, contractors and clients. It reviews data from road foundations (subgrades, granular capping and sub-base) and fully constructed in-service (thinly surfaced) roads, to demonstrate the flexibility of the LWD but also show that its determination of 'stiffness modulus' may differ from that of the conventional Falling Weight Deflectometer (FWD) to a varying extent. A series of laboratory investigations are presented that demonstrate the sensitivity to uniformity of plate/surface contact, and also limitations in the interpretation of peak displacement from the device. In conclusion, a good understanding of the device workings and careful specification of the test variables are required to both analyse the data correctly and permit comparison between data sets. The device is concluded to be a useful and versatile field quality control and pavement investigation tool, if an understanding of the device issues is considered by data users. INTRODUCTIONThis paper reviews the use of portable falling weight deflectometers (PFWDS) and the behaviour of the Lightweight Deflectometer (LWD) in detail. In this paper the term PFWD means any portable device for measuring a stiffness of material insitu, and the term LWD refers to the specific type of PFWD commonly known in Europe as the Prima, manufactured by Carl Bro (previously manufactured by Keros). The LWD is increasingly used for investigations of road construction materials and quality control. A background to the LWD development, a review of field data with a focus on correlation with the Falling Weight Deflectometer (FWD), and then specific laboratory investigations are presented. This paper is intended for reference by LWD users, consultants, material specifiers, contractors and clients.

Evaluation of PFWD as Potential Quality Control Tool of Pavement Layers

“…In other words, the relationship between CBR and PFWD modulus appears to be difficult to be defined for low-strength materials. This could be a reasonable agreement indicating poor correlation between CBR and E PFWD in another study where seventeen samples of all the CBR tests (eighteen samples) had values less than 25% (Seyman 2003). Indeed, CBR test is a strength evaluating testing method for soft materials.…”

“…Phillips and Freeman (2003), Nazzal (2003) and George et al (2009) showed that there is good correlation between these parameters; whereas, poor correlation was reported in some other research works (Seyman 2003;Phillips 2005). In addition, different correlations have been determined between the PFWD and FWD back-calculation moduli (Steinert et al 2006;George 2006).…”

“…In addition, different correlations have been determined between the PFWD and FWD back-calculation moduli (Steinert et al 2006;George 2006). Hence, the (Fleming et al 2007) other objective of this study is to assess the ability of PFWD to accurately measure soil strength in terms of traditional evaluation, namely CBR and FWD.…”

Pavement foundation stiffness testing – a new regime

“…Variation in compatibility/correlations between LWD devices and correlations to FWD stiffness has been observed, and these are observed to be material and site specific, as a function of the type of buffers and pulse duration, depth of material stressed and the position and size of foot that contacts with the ground. In addition, issues with the consistency of good plate to ground contact, and variation in operator test methodologies and basic operator errors can also cause variation in the data collected Fleming et al, 2007).…”

Developing Statistical Limits for Using the Light Weight Deflectometer (LWD) in Construction Quality Assurance

“…The LWD, which was first developed in Germany for use in pavement foundation construction, is receiving increased attention for use in quality control/quality assurance (QC/ QA) during pavement construction (Nazzal, AbuFarsakh, Alshibli, & Mohammad, 2007). The LWD has been evaluated extensively in several European countries, notably in the United Kingdom (Fleming, Frost, & Lambert, 2007). In the United States, the device has already been evaluated in several states, including Kansas, Louisiana, Minnesota, Montana, and Virginia (Davich, Camargo, Larsen, Roberson, & Siekmeier, 2006;Hosain & Apeagyei, 2010;Mooney & Miller, 2008;Nazzal et al, 2007;Puppala, 2008;Siekmeier et al, 2006).…”